1. Field of the Invention
Embodiments of the present invention relate generally to the fabrication of microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS), and particularly to the suppression of stiction during MEMS and NEMS fabrication.
2. Description of the Related Art
MEMS components are found in numerous applications, including inkjet printers, cell-phone microphones, digital projectors, pressure sensors, and accelerometers. MEMS, also referred to as Micro Systems Technology (MST), include devices ranging in size from the micrometer to the millimeter scale. NEMS devices are similar to MEMS, but significantly smaller in size—from the sub-micrometer scale down to the nanometer scale. MEMS and NEMS are distinguished from comparably sized electronic devices, such as integrated circuits, in that MEMS and NEMS include both electrical and mechanical components that are generally manufactured together using micro-machining techniques.
One example of a MEMS device is the digital micro-mirror device integral to digital light processing (DLP) technology. In a digital micro-mirror device, a pair of electrodes control the position of a micro-manufactured mirror mounted on a torsion hinge. Another example is a MEMS resonator, in which one or more mechanical beams are deflected by an electrostatic charge periodically applied to a drive electrode to induce vibration at a resonant frequency.
Due to their large surface to volume ratio, the behavior of MEMS devices is dominated by surface effects compared to volume effects. Surface effects include electrostatic, van der Waals, and capillary forces. Examples of volume effects include inertia and beam bending. Because of this, stiction of the microelectromechanical components of a MEMS device often occurs when these components come into contact with another surface. As used herein, “stiction” for a microelectromechanical structure is defined as the state of being stuck or frozen in a non at-rest position. For a MEMS resonator, some types of stiction are also referred to as “snap-down.” Stiction occurs whenever the restoring force of the microelectromechanical component is less than the stiction force produced by the unwanted contact with another surface. Such unwanted contact may be initiated by the high accelerations associated with mechanical shock of a MEMS device, liquid or other contamination either inside a MEMS device or on surfaces of a MEMS device, or deflection of a MEMS device's moving parts due to electrostatic charges accumulated on structures in the MEMS device.
Some MEMS devices, such as MEMS resonators, are manufactured with the same silicon fabrication technology used for producing microelectronics. In some cases, MEMS devices so produced are susceptible to experiencing stiction caused by accumulated static charges. This is because the requisite silicon fabrication technologies include methods, such as reactive ion etch, that may highly charge regions on the surface of a substrate during processing.